A capacitance sensor is generally positioned below a protective cover, in which an electrode A and an electrode B form a two-dimensional matrix intersecting with each other by designing a certain pattern. In the matrix, each touching region (as shown in FIG. 1) corresponds to one characteristic capacitance. A certain gap should be designed between the two electrodes so as to avoid short-circuit, and some suspended blocks are inserted between the electrode A and the electrode B to improve visual effect.
When one finger touches a touching device, the finger may generate capacitance C1&C2 with the electrodes A and B, respectively. Such a capacitance may vary the characteristic capacitance Cm between the electrodes A and B (as shown in FIG. 2, a value of the capacitance CM in each of the area in a 6*6 touching area) to be Cm′ (as shown in FIG. 3). The variation quantity of the characteristic capacitance before and after touching is represented by ΔC=Cm−Cm′ (as shown in FIG. 4). The variation value of capacitance caused by touching of the finger ΔC is about 100 (such a value is a dimensionless number converted by analog-digital conversation, without specifically illustrated, the capacitance in the present disclosure shares the same unit as such a value).
However, the touching device meets a complex noise scene in realism, which comprises power supply noise, LCD noise, system noise, external environment noise and so on. Superposing of these noises may lead to that there is a possibility of variation quantity of the characteristic capacitance between the two electrodes exceeding a trigger threshold. In the prior art, during a scanning cycle, a determination about whether it is a touching event is made by cooperating with a corresponding algorithm for filtering noise. However, the algorithm for filtering noise is generally complex and has an unfavorable effect of filtering noise.